Rainfall

Rainfall in April was average to above average across the Sydney region. The official site at Observatory Hill recorded 146.6 mm which is above the historic April average1 of 126.2 mm. There were 17 rain days during April well above the April average of 12, with rain recorded 13 days in a row from the 14th through to the 26th of April. This was the longest wet spell Sydney has experienced since a 15 day wet spell in March 2001. The wet spell resulted from persistent moist on-shore south to southeasterly winds directed by a high pressure system which moved very slowly from the Bight into the Tasman Sea.

Rainfall over the metropolitan area during April was highest in eastern and northern suburbs and lowest in the west. Totals ranged from 201.4 mm at Palm Beach on Sydney's northern beaches to a low of only 20.6 mm at Camden (Brownlow Hill) in the far south west.

The Warragamba Dam catchment recorded generally light rain during April which contributed towards maintaining steady storage levels.
Monthly totals over most of the catchment were around 20 - 50 mm with some isolated heavier falls of up to 183 mm at Katoomba on the catchment divide. Recent rainfall in Sydney's drinking
water catchments can be found on the Sydney Catchment Authority web site http://www.sca.nsw.gov.au/dams/rainfall.html.

Temperatures

Sydney experienced a cool April, with a mean maximum temperature of 21.5 °C which is 1.7 °C below the historic April average 1 making it the coldest April since 1983. The cooler temperatures were largely due to cloud cover and showers from persistent moist south to south easterly winds. A cold change that affected much of south eastern Australia saw the maximum temperature at Sydney Observatory Hill reach only 16.8 °C on the 28th of April. This was the coldest April day in Sydney since 1999.

Across the wider Sydney region mean maximum temperatures were between 20 and 22 °C. For many locations especially in western Sydney this was 2 to 3 °C below the historic average, and in some cases record or near record low average maxima for April. At Richmond the average maximum of only 21.3 °C was 2.9 °C below normal and the coldest on record (records since 1928). Liverpool recorded its 2nd lowest average maximum temperature on record for April and the coldest since 1983.

Sydney's April mean minimum temperature of 13.9 °C was also below the historic average 1 of 15.2 °C. Generally across the Sydney region minimum temperatures were between 1 and 2 °C below the historic average. At Camden, the average April minimum temperature of 9.3 °C was the 2nd lowest since records commenced in 1972 (lowest was 8.5 °C in April 2006).

Other phenomena

Associated with the persistent cloud cover was below average sunshine hours. Sydney recorded an average of only 6.1 hours per day, well below the historic April average of 6.9 hours.

Winds were generally from the south to south east for most of the month. The highest wind gust was 78 km/hr recorded at Richmond on the 27th.

Notes

This statement has been prepared based on information available at
9 am on Thursday 1 May 2008.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

1Averages: historic average temperatures for
Observatory Hill and Richmond are based on the period 1961 to 1990 which is a convention of the World Meteorological Organisation.
Average temperatures for Parramatta are based on all available
data, 1968 - 2007 and Camden 1972 - 2007. Rainfall averages
and extremes for Observatory Hill are based on all years of record
1859 - 2007.

A note about deciles: Deciles are used to give an element (in this case rainfall or temperature) a ranking. Deciles are calculated by arranging the totals in ascending order (from lowest to highest) then splitting them into 10 equal groups (thus the groups are called deciles). The first group would be in decile range one, the second group in decile range two, etc up to the highest annual totals (highest 10 per cent) being in decile range 10.

Normals are long-term averages based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 20 years of record for temperature and less than 30 years of record for rainfall, as they cannot then be calculated reliably.